1. Field of the Invention
This invention relates to a semiconductor device and a method of manufacturing thereof and in particular to a structure of a semiconductor device having a capacitor electrode of a semiconductor integrated circuit typified by a storage device or an information device.
2. Description of the Prior Art
For example, attention is focused on a simple stacked typed, fin, or tubular (cylindrical) structure as a capacitor structure having an extent not only in the horizontal direction, but also in the height direction to provide a sufficient capacitance in a limited space for high integration following 64-M DRAMs (dynamic random access memories). Further, a method of applying chemical treatment to a storage node electrode (a lower electrode of a capacitor), thereby forming microscopic asperities on the surface of the electrode for increasing the surface area is already designed to increase the capacitor capacitance.
FIG. 17 is a sectional view of a part of a semiconductor device when the surface of a capacitor electrode is roughened using a technique described on "dai42kai shunki ouyou buturi gakkai yokoushuu 2," 30p-R-16.
In FIG. 17, numeral 101 denotes a semiconductor substrate, numeral 102 denotes an impurity region selectively placed and formed on the surface of the semiconductor substrate 101, numeral 103 denotes an interlayer insulating film laminated on the surface of the semiconductor substrate 101, numeral 104 denotes a contact formed at a depth from the surface of the interlayer insulating film 103 to the surface of the semiconductor substrate 101 so as to abut the impurity region 102, and numeral 105 denotes a thick film storage node laminated on the surface of the interlayer insulating film 103 and electrically connected to the contact 104.
After the storage node 105 is formed, surface roughening is performed and asperities are formed on the surface of the side opposed to a cell plate later formed.
The surface roughening is performed as follows:
First, the storage node 105 is formed of phosphorus-doped polysilicon, then is activated by thermal treatment. Annealing is performed in a N.sub.2 atmosphere depending on the activation degree of impurity phosphorus in the storage node 105 before the surface roughening. Next, a thermal phosphoric acid is used to etch phosphorus doped in the storage node 105. Here, since phosphorus is easily segregated to grain boundaries of polysilicon, the grain boundaries are selectively etched and the surface is roughened.
It is seen that according to the surface roughening method described on "42-th Spring Ouyou Buturi Gakkai yokoushuu 2," 30p-R-16, the surface of a storage node of thick film stack type is roughened and the surface area can be increased to 1.4 times that before the surface is roughened.
However, application of the surface roughening method according to the prior art to a storage node of a tubular structure involves a problem. The storage node of thick film stack type shown in the prior art has a large film thickness and becomes a stable shape after the surface is roughened, but if the film forming the tubular storage node has a small thickness and the surface in the tubular portion is too much roughened, the strength as an electrode cannot be maintained and in an extreme case, the tubular portion falls down or peels off.
Especially in the case of the storage node, it is difficult to make a roughness of the surface through outer periphery, inner periphery of the tubular portion and a surface of horizontal portion, uniform. Thereby a reliable capacitor having accurate capacitance, can be obtained.
Further in the case of roughening a surface, since is difficult to control an etching depth, it is difficult to control a capacitance stable and accurately.
Even if a shape of the storage node can be controlled accurately, contact characteristic with a dielectric layer formed on the storage node is not sufficient. So it is required to make a surface state of the storage node uniform, to prevent a current concentration and to improve a contact characteristic.